Recent studies have indicated that functional recovery of locomotor function after spinal cord injury may be enhanced by performing repetitive stepping movements on a treadmill with a harness for partial body weight support with passive assistance provided by therapists. The putative mechanism that underlies this recovery is activity-dependent plasticity of neural circuits both in the spinal cord and in supraspinal centers. Although results in some subjects have been encouraging, in general, the functional gains that have been demonstrated from locomotor therapy are moderate and there is a high variability across subjects. We believe that the 'standard' form of this therapy (treadmill/harness with passive assistance from therapists) is soundly based on well established principles of motor learning, but the manner in which the therapy is delivered does not enable maximization of the therapeutic effect. We propose that locomotor therapy may be enhanced by: 1) producing sensorimotor patterns that are more 'physiological' - i.e. that include appropriately timed muscle contractions and are therefore more similar to sensorimotor patterns in the intact state and 2) generating movement patterns in a more repeatable manner. Our approach utilizes adaptive control of electrical stimulation to activate muscles in order to generate repeatable movements on the treadmill. We believe that the combination of appropriately timed contractions and repeatable movement patterns will result in an improved form of locomotor therapy. Furthermore, the adaptive nature of the control system may be used to encourage gradual increases in voluntary input, therefore providing a mechanism for weaning the individual from FES-assistance during locomotion. The long-term goal of this work is to develop a system that will provide a more effective and efficient form of locomotor retraining therapy. In this work, we will develop a technique that uses adaptive control of electrically-stimulated muscles to produce repeatable stepping movements with coordinated sensorimotor patterns of activity. The system will use transcutaneous neuromuscular stimulation to assist in movement generation while walking on the treadmill with partial body weight support provided by a harness. Adaptive control techniques will be used to automatically determine an appropriate set of stimulation parameters for a given individual and to automatically adjust the stimulation parameters to account for fatigue and/or motor retraining effects. The goals of the proposed project are to develop the adaptive system and to evaluate its ability to generate specified movement patterns. We will implement the adaptive system and experimentally demonstrate that it is capable of reliably producing stepping movements by individuals with spinal cord injury on a treadmill with partial body weight support. In future work (beyond the scope of this proposal), we will compare the efficacy of adaptive FES-assisted locomotor therapy with other forms of locomotor therapy.